The present invention relates generally to reciprocating pumps, and more specifically to reciprocating pumps having a transmission.
Electrically driven reciprocating pumps are well known in the art. They generally have an electric motor connected to a gear box which, in turn, is connected to a mechanism in the pump that converts the rotational motion into reciprocating motion. Depending on the potential output of the electric motor and the torque required for the pumping operation, a gearbox may be needed. For instance, a gearbox may permit a high speed, low torque input of an electric motor to be converted into a low speed high torque output for the pump.
Such a gearbox generally uses gears in a heavy, large, cast gearbox assembly, with the gears requiring constant lubrication. The gearbox needs to be large because the step down in speed from the shaft of the electric motor to the pump shaft is significant, in the range of 10:1 to 90:1. This requires multiple sets of gears of varying sizes to achieve the speed reduction. The very heavy and large assembly not only creates packaging issues, but also introduces maintenance concerns. For instance, the oil in such a gear box deteriorates over time. As a result, the gearbox oil must be monitored and serviced periodically.
Another problem with such typical gearboxes is adjusting output speed. The most common way to adjust output speed is to use a variable speed drive (VSD) to control the motor speed. This is functional, but forces the motor to operate off its peak efficiency when run at slower speeds. Combined with the fixed gear ratio in the gearbox, this limits the range of speeds at which the pump can operate. The VSD also may cause problems by inducing harmonic distortions in the electrical circuit it is tied into, it can create heat that needs to be dissipated, and which can be expensive. One potential solution is to remove the VSD altogether and to use a transmission between the motor and the pump. This would allow the motor to rotate at an efficient speed, but turning the gearbox into a transmission with multiple gear ratios would multiply the number of gears used as well as the size, weight and cost, creating still further disadvantages.
A traditional prior art one-way clutch transmission removes all the gears and requirements for heavy parts as well as adding the ability continuously change gear ratios. This allows the output speed of the transmission to be very accurately set without changing the motor speed. The drawback is that this type of transmission utilizes a significant number of linkages to achieve the same output as a geared transmission. All the linkages in the transmission transmit forces through pivoting joints that need to be lubricated and will ultimately need to be replaced.
The present invention addresses shortcomings in the prior art by providing an inexpensive, relatively maintenance free, transmission that is integrated into a reciprocating pump without using gears.